Recently, there has been growing interest in energy storage technologies. As energy storage technologies are extended to devices such as cellular phones, intensive research and development of electrochemical devices has been made, putting electrochemical devices as one of the subjects of great interest. Particularly, development of rechargeable secondary batteries has been the focus of attention. Recently, research and development of such batteries are focused on the designs of new electrodes and batteries to improve capacity density and specific energy.
Among currently available secondary batteries, lithium secondary batteries developed in the early 1990's have drawn particular attention due to their advantages of higher operating voltages and much higher energy densities than conventional aqueous electrolyte-based batteries, for example, Ni-MH, Ni—Cd, and H2SO4—Pb batteries. However, such lithium ion batteries suffer from safety problems, such as fire and explosion, when encountered with the use of organic electrolytes and are disadvantageously complicated to fabricate. In attempts to overcome the disadvantages of lithium ion batteries, lithium ion polymer batteries have been developed as next-generation batteries. More research is still urgently needed to improve the relatively low capacities and insufficient low-temperature discharge capacities of lithium ion polymer batteries in comparison with lithium ion batteries.
Meanwhile, conventional methods of preparing a cathode, an anode and a separator have been carried out by applying on each substrate an active material-slurry or an inorganic-slurry in which a solvent is contained, followed by drying, when forming an active material layer on the current collectors of the cathode and anode, or coating inorganics on the separator. Such a solvent is used for obtaining flexibility, proper dispersion of active materials and inorganic particles and appropriate viscosity.
However, according to conventional methods, purchase costs incurring depending on the use of solvents, additional costs that incur for handling and storing harmful solvents, as well as the reduction of a product yield that occurs due to a drying procedure after the coating of a slurry are all considered disadvantages.